Four wheel steering systems for use with motor vehicles having front and rear steerable wheels are known in the art. Typically, the front steerable wheels are manually controlled by the vehicle operator and the rear steerable wheels, mechanically or electronically are controlled, in response to the position of the front wheels and other vehicle operating parameters, such as vehicle speed. By adjusting the rear steerable wheels, vehicle handling can be improved.
U.S. Pat. Nos. 4,441,572, 4,645,025, 4,679,809 and 4,901,811 relate to four wheel steering systems wherein the steering angle of the rear wheels is determined based on parameters, such as sensed vehicle speed, front and/or rear wheel steering angles and the like. Specifically, the '811 reference discloses a vehicle steering system for adjusting tire characteristics. The vehicle comprises front wheels, each being equipped with a front tire; and rear wheels, each being equipped with a rear tire having a rear tire characteristic which is different from the front tire characteristic. The vehicle also comprises a rear wheel steering system for steering the rear wheels and controlling means for adjusting the rear tire characteristic by steering the rear wheels in a predetermined first cornering condition of the vehicle.
U.S. Pat. Nos. 4,412,594, 4,690,431, 4,718,685 and 5,019,982 relate to four wheel steering systems wherein the rear steering angle is determined based on inputs including a signal representative of an actual vehicle motion variable, such as yaw rate or lateral acceleration. More particularly, the '982 reference discloses a method of controlling the rear wheels of a four wheel steering vehicle having front road wheels which can be turned by steering action, rear wheels which can be turned in response to the turning of the front wheels and means for detecting lateral acceleration applied to the vehicle. This arrangement allows for variable control of the steer angle ratio of a rear steer angle relative to a front steer angle based on the lateral acceleration.
U.S. Pat. Nos. 4,865,146 and 5,014,801 disclose a four wheel steering system wherein the rear steering angle is calculated based on vehicle parameters, such as steering torque, and U.S. Pat. No. 4,936,401, assigned to the assignee of the present invention, discloses a system for steering front and rear steerable wheels of a vehicle.